The invention relates to a process for cooling dispersions and liquids, which are first deodorized in a vessel.
It is known to prepare polymer dispersions by suspension polymerization or emulsion polymerization. The products usually still contain undesirable volatile organic components such as residual monomers resulting from incomplete reaction, impurities from the starting materials, decomposition products of the initiators or low molecular weight products from side reactions. These compounds are referred to hereinafter by the collective term "residual volatiles". In the Commission's decision 96/13/EC regarding the definition of environmental criteria for issuing the EC environmental symbol for interior paints and coatings of Dec. 15, 1995, these residual volatiles are divided into volatile organic compounds (VOC) and volatile aromatic hydrocarbons. In both cases these are organic compounds having a boiling point (or initial boiling point) of at most 250.degree. C. under atmospheric pressure conditions. The volatile aromatic hydrocarbons in this context have at least one aromatic nucleus in their structural formulae. The collective term "residual volatiles" used herein refers to all such organic compounds having a boiling point (or initial boiling point) of at most 250.degree. C.
Residual volatiles can be present not only in dispersions, but also in liquids. For example, when a dispersion formed by emulsion polymerization is broken by means of an electrolyte or acid, at least some of the residual volatiles remain in the liquid which separates from the polymer. The residual volatiles may present problems in connection with environmentally compatible disposal of such liquids. Furthermore, residual volatiles are undesirable for many applications of dispersions or suspensions, for example in the food or cosmetics sector or for interior applications, and what is aimed for is substantially complete elimination of these.
Dispersions or liquids are therefore subjected to a treatment which removes the residual volatiles. This treatment is referred to as deodorization. Various methods and apparatuses are known for this purpose: Apart from chemical processes, which usually, however, affect only the unsaturated compounds, these are predominantly stripping processes in which a stripping gas is passed through the suspension or dispersion. The stripping gases used are air, nitrogen, supercritical carbon dioxide, ozone or steam. Apparatuses in which the suspension or dispersion is treated with the stripping gas may take various forms. In the simplest design, the apparatus comprises a vessel which holds the suspension or dispersion and into which the stripping gas is introduced by means of lances or valves at the vessel bottom.